Ductile case-hardened steels



Oct. 29, 1968 J. T. GULLIKSEN ETAL 3,408,237

DUCTILE CASE-HARDENED STEELS Filed March 16, 1967 INVENTORS John 7.Gu/lf/rsen Alfred E. Oldaker 5 3; JQBOIda ATTORNEYS United States Patent3,408,237 DUCTILE CASE-HARDENED STEELS John T. Gulliksen, Peekskill, andAlfred E. Oldaker, Poughkeepsie, N.Y., and Frank J. Bolda, Raleigh,N.C., assignors to International Business Machines Corporation, Armonk,N.Y., a corporation of New York Continuation-impart of application Ser.No. 379,139, June 30, 1964. This application Mar. 16, 1967, Ser. No.633,651

2 Claims. (Cl. 148-155) ABSTRACT OF THE DISCLOSURE Steel materialshaving discontinuous case-hardened areas surrounded by continuousductile areas, materials having series of very small case-hardened areasand materials fabricated from ductile case-'hardenable steels havin oversurface regions thereof a case-hardened pattern imparting to thatsurface the hardness and wear characteristic of case-hardened steel andthe bending and ductility characteristics of unhardened ductile steelare described herein.

This is a continuation-in-part of application Ser. No. 379,139, having asimilar title and filed by the same inventors on June 30, 1964, nowabandoned. It has been known heretofore to selectively case harden softsteel so as to facilitate the working and fabrication of such steel. Sofar as is known, the prior art has not yet developed a discontinuouscase-hardened pattern over a large area, or all, of one or more surfacesof a fabricated ductile case-hardenable steel material, such asfabricated carburizing and nitriding carbon-containing steels, so as tomake optimum use of the ductility, of the wear resistance, and of otherattributes of case-hardened steels.

Selective case hardening which is known in the prior art has resulted insteel plates incapable of being further worked or has required precisionin leaving areas to be worked unhardened. The present invention, on theother hand, discloses a method of mass producing case-hardened materialwhich may be worked and bent at all points.

It is an object of this invention to provide hardware, sheet material,and like fabricated materials having both a hard wearing Surface andductility.

More particularly, it is an object of this invention to provide acase-hardened patterned surface on a carboncontaining case-hardenablesteel part which is highly resistant to wear and yet retains enoughductility to allow bending, forming, straightening or the like withoutdetrimental effects on the part, such as induced cracking or impairmentof its wearing characteristics.

More specifically still, it is an object of this invention to provide anover-all pattern of case-hardened wearing surfaces on hardware parts andother materials fabricated from normally soft and ductile low carbon andnitriding steels without sacrificing ductility.

It is a special object of this invention to provide a process forproducing a desired over-all substantially uniform pattern of unhardenedand case-hardened regions on a soft, ductile fabricatedcarbon-containing steel material which is case-hardenable bycarburizing, nitriding, or the like.

It is another special object of the invention to provide fabricatedductile case-hardenable steel materials having a raised pattern ofdiscontinuous case-hardened steel in a continuous matrix of theunhardened material.

It is yet another special object of the invention to pro vide anover-all pattern of unhardened and case-hardened regions on a surface ofa fabricated case-hardenable steel in which the case-hardened regionsoccupy the major portion of the surface. It is a still further specialobject of the invention to provide an over-all uniform case-hardenedpattern of micromim'ature spots on the surface of ductile steel parts.

The foregoing and other objects, features and advantages of theinvention will become apparent from the more detailed description ofspecial embodiments of the invention as illustrated in the accompanyingdrawings.

FIGURE 1 is a reproduction of a photomicrograph of a portion of asubstantially uniform pattern of carburized case-hardened spots on aplate of carburizing steel, prior to the removal of a copper maskant, inwhich the holes in the maskant have an average diameter of about 0.005

*and an average distance of 0.015 from center-to-center.

FIGURE 2 is a diagrammatic representation of FIG- URE 1 after theremoval of the maskant showing a carburized case, which is about 0.002"thick, and illustrating the lateral spread of the case-hardened areas.

FIGURE 3 is a diagrammatic representation similar to FIGURE 2 with thelateral distance from center-to-center being twice that of FIGURES 1 and2, and in which casehardened carburized discontinuous spots aresubstantially square in shape and occupy a decidedly predominantproportion of the surface of the sheet.

Broadly viewed, the objectives of the invention are obtained by firstoutlining a pattern of continuous and discontinuous regions over atleast one surface of a fabricated ductile case-hardenable steelmaterial, by covering a part only of the surface of the material with amaskant which inhibits or prohibits case hardening, leaving uncoveredthe pattern to be case hardened, then case hardening the uncoveredpattern, and thereafter removing the maskant to leave a pattern ofcase-hardened and unhardened regions.

Known methods of case hardening may be used including carburizing,nitriding, cyaniding, carbonitriding, and the like. carburizing, orcarbonitriding and nitriding are preferred. Flame and inductionhardening are also applicable, providing a pattern of continuous anddiscontinuous regions over the surface of a fabricated material is firstcase carburized.

In the case hardening of the sheet illustrated in FIG. URE 1, copper wasused for the known purpose of the stopping-01f of carburizing on afabricated sheet of A181 C-lOlO carbon steel, which is known to be welladapted for carburizing. First, the sheet was thoroughly cleaned, andthen it was dipped in a photoresist. A negative pattern being opaque tothe monochromatic light used, and having therein holes corresponding tocarburized dots 10, described below, was placed over one side of thesheet and the pattern was exposed to monochromatic light for a period oftime sufficient to fix a pattern of dots corresponding to the holes inthe negative pattern. Then the pattern of dots was developed in adeveloper solution, and the unexposed photoresist was removed in theusual manner, leaving only the developed dots having a radius of about0.005. Next, after cleaning in a known way, the sheet was immersed in anelectrolytic copper plating bath to electrodeposit a continuous layer ofcopper all over one side of the sheet and a continuous region of copper12 surrounding the developed dots on the other side of the sheet. After50 minutes residence in the bath, and under the conditions set outbelow, a copper plating 0.7 mil thick was deposited.

Plating bath and plating conditions Copper cyanide 6 Potassium cyanideoz./gal.. 9.7 Potassium hydroxide oz./gal 1.0 Sodium potassium tartratepercent by vol 6 Bright copper makeup do 2 Temperature F-.. 130 Currentdensity amps 25 Cathode rod agitation ft./rnin 20 Cyaniding bath PercentSodium chloride Sodium cyanide 50 Barium carbonate 25 After the casehardening was obtained, the copper was stripped from the sheet in aknown way in a chromic acid strip bath. Upon removal of the copper, itwas apparent the carbon had penetrated laterally as well as downwardlyso that the carburized dots 10 had the dimensions shown in FIGURE 2.

Desired variations in the extent and depth of the carburized regions canbe obtained by varying the period of treatment or the temperature of thebath or both.

By using a negative pattern having uniformly distributed holes with adiameter of 0.010" and centers 0.015 apart, a pattern of carburized dots10 occupying about 60% of the total working surface is obtained. Thedots are surrounded by a continuous pattern of unmodified sheet material12a as diagrammatically represented in FIGURE 2. As shown in FIGURE 3,when it is desired to carburize even larger proportions of the surfaceof the fabricated material, a negative pattern may be used provided withsquare or other rectilinear holes corresponding to the carburizedcase-hardened wafiie design 14. These larger case-hardened designs,having unhardened channels therein, afford an excellent means forsupplying surface lubricants.

It is obvious the techniques set out above may be used to develop apattern of case-hardened regions over as many, or as much, of thesurfaces of the fabricated material as may be desired.

It is apparent also, the same techniques set out above may be used forcase hardening by nitriding known nitriding grades of carbon-containingalloy steels as, for example, ASTM A-355, class A. As is known, suchsteels preferably contain a small percentage of aluminum or chromium tofacilitate nitriding. In such a process the material, or parts, may beheated in an atmosphere of ammonia gas and dissociated ammonia mixed insuitable proportions, or in contact with a nitrogenous medium. Theprocess is carried out below the transformation range for the steelused, and no quenching operations are necessary. A suitable nitridingcycle is carried out at a temperature of 950-1050 F. The flow of ammoniais adjusted so as to maintain a concentration of 70 percent ammonia andpercent nitrogen and hydrogen in the exhaust gas.

As used herein microminiature has the conventional definition of verysmall. Where microminiature regions of case hardening are notadvantageous, or necessary, as often is the case, other means ofcarburizing may be used as, for example, covering desired regions withcarbonaceous cements and then heating to carburizing temperatures andthereafter quenching. Also, where larger case-hardened areas aredesired, the copper may be electrodeposited by using other types ofmaskant during the electrodeposition of the copper on the fabricatedmaterial, such as paints or waxes, to mask the electrodeposition of thecopper.

Where it is desirable to have uniform wear properties and/or uniformductility, it is necessary to have a uniform pattern of case-hardenedand unhardened regions over the surface of the fabricated material. Itis apparent, however, that the principles of this invention may be usedto provide irregular patterns of hardened and unhardened regions overthe surface of the material.

The advantages of this invention are obtained by having patterns ofductile steel over the surface of a casehardened object, whereby theobject may be bent at all points for the construction of a case-hardenedpart. When patterns of case-hardened and unhardened areas are uniform,case hardening may be carried out in mass production without regard forthe particular area of a blank to be bent.

The optimum advantages of this invention are obtained for mostapplications where a substantially uniform discontinuous pattern ofcase-hardened miniature dots is provided surrounded by a continuouspattern of unhardened ductile material. In this way, optimum ductilityis retained while permitting the development over very large proportionsof the fabricated material very hard and wear resistant patternedregions. The minimum size of the dots is limited only by the availableart work or maskants. In general, the illustrative embodiments shownherein, wherein the radius of the hole in the maskant is 0.005" and thecenters are 0.015" apart, represent a'bout the minimum practical sizefor carburizing for the process it most advantageously practiced whenthe carburized regions do not merge. Since carburizing to a depth of0.002" usually is desirable, if not necessary, it will be apparent thecarburizing regions will merge when carburizing through such a coppermask to a depth substantially exceeding 0.002. For the purposes of thisinvention the most useful case-hardened dots may be considered dots witha maximum dimension of 0.100". Uniformly distributed case-hardened dotshaving a radius between 0.005 and 0.010" are preferred where uniformity,ductility and formability are desired together with hardness and wearresistance. In many applications dots having a diameter of 0.050" arequite small enough.

It will be understood, of course, the principles of this invention maybe used to develop case-hardened patterns having desired dimensions evenexceeding 0.100". For instance, where lubrication is a more importantobjective and ductility is of less importance, case-hardened patternshaving case-hardened regions With dimensions greatly exceeding 0.100"may prove quite satisfactory.

Thus fabricated materials having surface patterns of case-hardened andunhardened regions over a surface thereof, as described above, have anumber of advantages over like fabricated materials now readilyavailable, including: V

(1) Flat parts can be roller straightened, where hand straightening hasheretofore been considered necessary.

(2) Forming operations are possible which are not possible with anover-all hardened case.

(3) Microminiature case-hardened regions of high density are madeavailable.

(4) Less expensive ductile carbon steels can be used where moreexpensive case-hardened steels have heretofore been considerednecessary.

(5) When the discontinuous regions are carburized to form elevatedcase-hardened regions, the continuous regions form excellent lubricationchannels; and, where case-hardened regions are not raised, theunhardened regions wear in and may also serve as lubricating regions, orfor like purposes.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is: 1. A case-hardened steel product comprising apartially case-hardened portion having at least one face defining aplurality of isolated uniformly distributed casehardened areas havingmaximum surface dimensions of from approximately 0.005 to 0.010 inch,and having centers of such areas spaced approximately 0.015 inch apart.

2. The process for producing a partially case-hardened steel producthaving at least one face defining a plurality of isolated case hardenedareas comprising:

cleaning at least one face of a steel blank; coating the at least oneface with a photoresist; exposing discontinuous regions of thephotoresist coating with a predetermined pattern of radiant energy;

washing away unexposed portions of the photoresist coating, leaving acontinuous bare area of the at least one face;

electrodepositing a copper coating on the bare area of the at least oneface;

removing exposed areas of the photoresist coating,

thereby exposing predetermined discontinuous portions of the at leastone face of the blank, said discontinuous portions having maximumsurface dimensions of from approximately 0.005 to 0.010 inch, and havingcenters of such areas spaced approximately 0.015 inch apart;

case-hardening discontinuous exposed portions of the face; and

removing the copper coating, thereby providing a product havingdiscontinuous case-hardened regions and continuous unhardened regions.

References Cited UNITED STATES PATENTS 728,217 5/1903 Falk 148-391,072,660 9/1913 Shore 148-19 1,759,690 5/1930 Fleckenstein et al.148-14 3,122,817 3/1964 Andrus 148-187 X 3,184,823 5/1964 Little et al.148-187 X 3,193,418 7/1965 Cooper et al. 148-187 3,231,421 1/1966Schmidt 148-187 X OTHER REFERENCES Metals Handbook, 1948 ed., publishedby ASM, relied on pages 693 and 694.

CHARLES N. LOVELL, Primary Examiner.

